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IT 212 002 How Computers Work May 3, 2007

IT 212 002 How Computers Work May 3, 2007. Wireless LAN, Cell Phones, Bluetooth Final Review. Lecture Agenda. Chapter 26: How Wireless Sets PCs Free Final Exam Review. Chapter 26: How Wireless Sets PCs Free. Wireless LAN.

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IT 212 002 How Computers Work May 3, 2007

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  1. IT 212 002How Computers WorkMay 3, 2007 Wireless LAN, Cell Phones, Bluetooth Final Review GMU IT 212 - Spring 2007

  2. Lecture Agenda • Chapter 26: How Wireless Sets PCs Free • Final Exam Review GMU IT 212 - Spring 2007

  3. Chapter 26: How Wireless Sets PCs Free GMU IT 212 - Spring 2007

  4. Wireless LAN • A wireless local area network (WLAN) is a LAN that does not use wires as a connection medium • Ethernet example of LAN • Wi-fi, also known as IEEE 802.11, is an example of a WLAN • There are many versions of the IEEE 802.11 standard including: • 802.11b • 802.11a • 802.11g • 802.11n (coming soon) GMU IT 212 - Spring 2007

  5. Current Flavors of Wi-Fi GMU IT 212 - Spring 2007

  6. Wireless Access Points/Routers • For home use, typically have a wireless router or wireless access point (AP) • Wireless router = Wireless access point plus a router • Wireless router allows you to share one DSL/cable modem connection among several wireless computers • Wireless access point needs a separate router to share broadband connection • Wireless router connects directly to DSL/cable modem via Ethernet cable • Also possesses a switch (4-port) which allow you to connect wired desktop computers to the network GMU IT 212 - Spring 2007

  7. Wireless nodes on the network are called stations Laptops, PDAs, printers, digital cameras, etc. A wireless network adapter is used to connect to the wireless LAN PC card adapter USB adapter PCI adapter (desktops) Built-in adapter Has unique MAC address Wireless Stations GMU IT 212 - Spring 2007

  8. Wireless Protocol • Wireless station broadcasts probe request • Discovers which 802.11 APs in range • If an AP is within that range, the AP picks up the probe request and broadcasts an acknowledgement including its service set identifier (SSID) • The two stations go through a process that involves authentication • The AP and the station send packets to each other using specific addresses • Extension points may be used to extend the coverage of a wireless network • Point-to-point (computer-to-computer) networks are also possible for Wi-fi GMU IT 212 - Spring 2007

  9. Securing your WLAN Access Point • The following measures can all be broken, but offer a certain measure of security • Disable broadcast of SSID • Node must ask “Is Bob there?” to get a response • Normally asks “Is anyone there?” • Apply MAC filtering • Limit which MAC addresses can access your network • Apply encryption with WEP (wired equivalent privacy) • Use highest number of bits (128 bits) • Encrypts data traveling between station and access point GMU IT 212 - Spring 2007

  10. Cell Phones • -1983 Motorola DynaTEC Cell phone • -Around 38 ounces (1.75 pounds) • -10 inches tall • -2007 Motorola Razr • -Around 3.3 ounces • -3.8 inches tall GMU IT 212 - Spring 2007

  11. Base station covers a certain area called a cell Each base station connected to a switching center called the Mobile Terminal Switching Office (MTSO) MTSO connected to public switched telephone network When a mobile user turns the cell phone on, the cell phone communicates with the base station over a channel called the control channel The cell phone listens to the System Identification Code (SIC) that is broadcast over the control channel The SIC gives the cell phone information regarding the base station The cell phone also sends a registration request over the control channel which is passed over to the MTSO The MTSO contains subscriber info The MTSO is also responsible for billing the user Has the ability to assign which frequencies the mobile units may use to communicate with the base station MTSO Mobile Telephone Switching Office PSTN Public Switched Telephone Network Cell Phone Operation GMU IT 212 - Spring 2007

  12. Base station Mobile user Cell Phone Operation • Neighboring base stations use different communication frequencies to avoid garbled communications • As phone moves from one cell to another • Signal grows weaker • Neighboring station monitors strength on other frequencies, not only its own • When next station signal is stronger than current station, stations coordinate to transfer call on new frequency • Called a handoff GMU IT 212 - Spring 2007

  13. Analog versus Digital • Most cell phones today are digital but earlier ones were analog • Analog send analog signals to base station using carrier radio waves • Digital cell phone digitize audio signals using ADC circuits and radio wave carriers to send information to base station • Analog phones higher power than digital GMU IT 212 - Spring 2007

  14. FDMA vs TDMA vs CDMA • Multiple access = method to share a resource over many users • FDMA = frequency division multiple access • Users are separated in frequency i.e. mobile phones communicate at different frequencies than the others within each cell. • Analog phones • TDMA = time division multiple access • User are separate in time slots, can only communicate in allotted time slot • Used by GSM (Global System for Mobile Communication) phones • US Carriers: Cingular, T-Mobile • CDMA = code division multiple access • Users simultaneously use all frequencies and time slots available, assigned codes which do not interfere with one another • US Carriers: Verizon, Sprint www.owlnet.rice.edu/~elec301/Projects01/cdma/compare.html GMU IT 212 - Spring 2007

  15. GSM versus CDMA • Most of the world uses GSM • SIM (subscriber identity module) card contains user account information, address book, etc. • To use phone overseas… • Phone must be unlocked (i.e. can use any SIM card) • Make sure frequencies compatible: quad-band phone • US: 850 MHz,1900 MHz • Europe: 900 MHz, 1800 MHz • Next generation, moving to 3G (currently 2G or 2.5G) data services • Three competitors, all based on CDMA • CDMA2000: based on 2G CDMA • WCDMA: Wide-band CDMA; new European standard • TD-SCDMA: Time-division Synchronous Code-Division Multiple Access, in China • 3G networks have potential transfer speeds of up to 3 Mbps GMU IT 212 - Spring 2007

  16. Bluetooth • Bluetooth is a standard protocol for connecting wireless devices to each other located within a close vicinity • Harald Bluetooth is a Danish king who unified Scandinavia • Bluetooth devices comprise a radio module that incorporates the Bluetooth protocol • The range is limited to about 30 feet and data rate to a maximum of around 1Mbps • The link manager is a piece of software in the Bluetooth device to set up communications with other devices and to send/receive signals to/from them • Bluetooth devices may operate in a variety of modes including: • Standby, Page, Inquiry, Park and Hold • Bluetooth security issues GMU IT 212 - Spring 2007

  17. Bluetooth • Uses Frequency Hopping Spread Spectrum • Radio transmissions between devices “hop” between 79 different frequencies • Change frequencies 1,600 times per second • Hopping done to minimize interference • Transmit at 1 mW • Killer app: Bluetooth headsets GMU IT 212 - Spring 2007

  18. Final Exam Review GMU IT 212 - Spring 2007

  19. Final Exam • Open book, open notes • True/false, multiple choice, short answer • Students required to bring scantron form 882-E and a number 2 pencil!!! GMU IT 212 - Spring 2007

  20. Chapters from book to review • How Computers Works, 8th Edition • This semester we covered: • Chapters 1-19 • Chapters 21-22 • Chapters 24-27 • You are responsible for textbook material for topics covered in class GMU IT 212 - Spring 2007

  21. Review of lecture topics GMU IT 212 - Spring 2007

  22. Goals of the course • Upon the successful completion of this course, the student will be able to: • Describe the basic components of today’s personal computer and how they function together • Understand some of the historical developments that have resulted in today’s personal computers • Understand the basic operation and function of today’s personal computer • Understand what the Internet is and some of the historical developments that resulted in its creation GMU IT 212 - Spring 2007

  23. Jan 25—Introduction & Syllabus, History • Define computer • A programmable machine that inputs, processes and outputs data. • Any device capable of processing information to produce a desired result. No matter how large or small they are, computers typically perform their work in three well-defined steps: (1) accepting input, (2) processing the input according to predefined rules (programs), and (3) producing output. • In general, a device that uses digital technology to process and manipulate information. • An electronic device that stores, retrieves, and processes data, and can be programmed with instructions. A computer is composed of hardware and software, and can exist in a variety of sizes and configurations.  GMU IT 212 - Spring 2007

  24. Four Functions of a Computer A computer has four functions: Storage Input Processor Output GMU IT 212 - Spring 2007

  25. History of computers • In 1837, Charles Babbage designed a fully programmable mechanical computer that he called "The Analytical Engine". • Large-scale automated data processing of punched cards was performed for the US Census in 1890 • A succession of steadily more powerful and flexible computing devices were constructed in the 1930s and 1940s, adding key features seen in modern computers. • The use of digital electronics (largely invented by Claude Shannon in 1937), more flexible programmability were vitally important steps • The US Army's Ballistics Research Laboratory ENIAC (1946) • EDSAC: first computer to implement the stored program (von Neumann) architecture (1952). • Vacuum tube-based computers were in use throughout the 1950s, • Replaced in the 1960s by transistor-based devices • Smaller, faster, cheaper, less power and more reliable • By the 1970s, integrated circuit technology • Creation of microprocessors such as the Intel 4004 • By the 1980s, computers became sufficiently small and cheap to replace simple mechanical controls in domestic appliances • Computers became widely accessible for personal use by individuals • Home computers and personal computers. • Widespread growth of the Internet since the 1990s GMU IT 212 - Spring 2007

  26. Feb 1—Hardware, Wake-up Process, Boot-Up, Operating Systems • Inside a PC case • Motherboard (see textbook for contents) • Power supply • Hard Disk Drive • Media Drives: CD ROM, DVD ROM, Tape, USB Flash, Floppy • IDE Controller: disk drives • AGP, PCI-E • Video Card • Sound Card • RAM • Clock • BIOS • Microprocessor (CPU) • Heat Sink and Fan • Buses • USB • Keyboard • Network Controller • Parallel Port • Serial Port • Modem GMU IT 212 - Spring 2007

  27. Operating Systems • An operating system (OS) is a computer program that manages the hardware and software resources of a computer. Performs basic tasks such as • controlling and allocating memory • prioritizing system requests • controlling input and output devices • facilitating networking • managing files • May provide a graphical user interface for higher level functions • It forms a platform for other software • Discussed Windows, Mac, Unix/Linux GMU IT 212 - Spring 2007

  28. How a PC Wakes Up: 2 steps • Power-On Self Test (textbook pp. 24-25) • From turn on of power switch to transferring control from BIOS to operating system (OS) on hard disk • Disk Boot (textbook pp. 26-27) • After POST, processor executes program contained on hard drive’s boot sector for OS to take control • Continues until Windows logon screen GMU IT 212 - Spring 2007

  29. Hardware and Software Work Together • The operating system quickly evolved into an all-encompassing bridge between your PC and the software you run on it • Device driver • A device driver is a specific type of computer software, typically developed to allow interaction with hardware devices. • EIDE—hard disk driver • Hardware interrupts • How Plug and Play Works GMU IT 212 - Spring 2007

  30. Feb 8—Semiconductors, Transistors, RAM, Microprocessors Video Card • North Bridge • Memory (RAM) • CPU • Video Card • Frontside Bus (FSB) fast between RAM and CPU • Backside Bus, not shown, connects CPU to L2 cache • South Bridge connects other I/O such as disk drives, sound cards, Ethernet, etc. CPU Hard Drive GMU IT 212 - Spring 2007

  31. Plug and Play Rules GMU IT 212 - Spring 2007

  32. Windows Registry • Every operating system and application needs a place to store configuration settings and user preferences • MS-DOS uses CONFIG.SYS • DOS programs made own arrangements for user settings • Windows originally used INI files • Read and written using special routines • Windows had one configuration file, SYSTEM.INI, used for all the internal settings • Plus another, WIN.INI, for user preferences • Each application had an INI file • INI files were slow to access and limited to 64Kb • Unsuited for the 32-bit versions of Windows • So for Windows NT and Windows 95 Microsoft introduced the Registry • A database for storing and accessing configuration data • Organized for fast and efficient access • Data is stored in a hierarchical manner like the folders on a hard disk • Registry data that is currently in use is cached to provide better performance GMU IT 212 - Spring 2007

  33. Binary Arithmetic, Transistors • The simplest arithmetic operation in binary is addition. Adding two single-digit binary numbers is relatively simple: • 0 + 0 = 0 • 0 + 1 = 1 • 1 + 0 = 1 • 1 + 1 = 10 (carry:1) • Multiple bits • 1 1 1 1 1 (carry) • 0 1 1 0 1 • + 1 0 1 1 1 • ------------- • 1 0 0 1 0 0 • A transistor is the basis of integrated circuits, works as a switch GMU IT 212 - Spring 2007

  34. Feb 15—Programming Languages, How Windows Works, How Applications Work • PC computer memory is divided into segments, • 64 kilobytes each (65,536 bytes, to be exact) • Segment register in microprocessor indicates segment is to be accessed • Segment 0 • Contains memory pointers, device drivers, buffers, input/output ports, and other essential information required by the computer and its operating system • Segment 0 contains 65,536 memory addresses GMU IT 212 - Spring 2007

  35. Memory Map of Segment 0 GMU IT 212 - Spring 2007

  36. Mar 1, Mar 22—Long Term Memory, Disk Drives, Optical Storage • Volatile vs Non-Volatile memory • Volatile memory does not retain its information without constant power • Non-Volatile maintains information indefinitely • Magnetic Storage/Hard drives • Chapters 9-11 in textbook • Optical drives • Chapter 12 in textbook GMU IT 212 - Spring 2007

  37. Magnetic Storage • Media used in removable magnetic-storage devices is coated with iron oxide • A ferromagnetic material • If you expose it to a magnetic field it is permanently magnetized • The media is typically called a disk or a cartridge • The drive uses a motor to rotate the media at a high speed • Accesses (reads) the stored information using small devices called heads • Each head has a tiny electromagnet (an iron core wrapped with wire) • The electromagnet applies a magnetic flux to the oxide on the media • The oxide permanently "remembers" the flux last saw • During writing, data signal sent through a coil to create a magnetic field • At the gap, the magnetic flux forms a fringe pattern • The flux magnetizes the oxide on the media • During reading, the read head pulls a varying magnetic field across the gap • Creates a varying magnetic field in the core and a signal in the coil GMU IT 212 - Spring 2007

  38. Mar 29—Kernels and Routines,Bandwidth, UPS, Ports, SATA, USB • DLL = Dynamic-Link Library • A library of executable functions or data that can be used by a Windows application • A DLL provides one or more functions • A program accesses the functions by creating a static or a dynamic link to the DLL • A static link remains constant during program execution • A dynamic link is created by the program as needed • A DLL can be used by several applications at the same time • Some DLLs are provided with the Windows operating system and available for any Windows application • Other DLLs are written for a particular application and are loaded with the application • DLL is Microsoft's implementation of the shared library concept in the Microsoft Windows and OS/2 operating systems • Usually have the file extension DLL, OCX (for libraries containing ActiveX controls), or DRV (for legacy system drivers) • DLL file formats are the same as for Windows EXE files • DLLs can contain code, data, and resources, in any combination. GMU IT 212 - Spring 2007

  39. Application Program Interface (API) • A set of routines, protocols, and tools for building software applications • A good API makes it easier to develop a program by providing all the building blocks • A programmer puts the blocks together • Most operating environments, such as MS-Windows, provide an API • Programmers can write applications consistent with the operating environment • Guarantee that all programs using a common API will have similar interfaces GMU IT 212 - Spring 2007

  40. Registry • A database used by the Windows operating system to store configuration information • The Registry consists of the following major sections: • Roots - file associations and OLE information (Object Linking and Embedding) • Users Preferences - all preferences set for current user • User Information - all the current user information for each user of the system • Local Machine Settings - settings for hardware, operating system, and installed applications • Current Configuration - settings for the display and printers and other devices • Dynamic Data - performance data • Most Windows applications write data to the Registry • You can edit the Registry directly by using the Registry Editor • regedit.exe provided with the operating system • Errors in the Registry could disable your computer. GMU IT 212 - Spring 2007

  41. Bandwidth, UPS • Analog to digital converters • Digital to analog converters • Uninterruptable Power Supplies • Voltage surges and spikes - Times when the voltage on the line is greater than it should be • Voltage sags - Times when the voltage on the line is less than it should be • Total power failure - Times when a line goes down or a fuse blows somewhere on the grid or in the building • Frequency differences - Times when the power is oscillating at something other than 60 Hertz GMU IT 212 - Spring 2007

  42. Ports • A port serves as an interface between the computer and other computers or devices • Physically, a port is a specialized outlet to which a plug or cable connects • Serial • Parallel • SATA • USB GMU IT 212 - Spring 2007

  43. Apr 19—LAN, Internet, TCP/IP, DSL, Cable Modems • Local area network (LAN) • A network which connects computers together in a small geographic region (office, home, etc.) • Designed to share resources on a network • Example: sharing a printer at home • Can be wired or wireless • Topology: bus, ring, or star • Network model: client/server or peer-to-peer • Physical components: NIC card, wiring GMU IT 212 - Spring 2007

  44. Ethernet • Ethernet is the most common LAN today • Ethernet operates on the physical layer (layer 1) and data link layer (layer 2) • Most common installations of Ethernet (home, office) use: • CAT5/6 twisted pair cable • RJ-45 connectors • Communicate via Ethernet packets • NIC card has MAC address • 48 bit, represented in Hex 02608CBBDCA7 • IEEE assigns unique address • Permanently attached • This is a “layer 2” address • Ethernet Packet • Protocol called Carrier Sense Multiple Access with Collision Detection (CSMA/CD) GMU IT 212 - Spring 2007

  45. Hub vs. Switch vs. Router • Hub • Broadcasts what it receives on one port to all ports within a single network • Dumb device • Physical layer device (layer 1) • Switch • A “smart” hub: performs same function of a hub, just does the job better • A switch reads the MAC address of the packet and transmits the packet to the port that leads to the node it is addressed to (or can broadcast also) • Data Link layer device (layer 2) • Router • Connects different networks (i.e. different LANs together) by reading IP address • Often, when you buy a router it includes a switch • Internet layer device (layer 3) GMU IT 212 - Spring 2007

  46. Connecting to the Internet • Modems • Most recent type of modems are 56K, or V.90 that are able to carry data at a maximum data rate of 56Kbps • Digital Subscriber Line (DSL) or xDSL is a technology for sending high speed digital data across analog telephone lines • Unlike regular dial-up modems, you do not need to dial up, the connection is always on • Also, the phone lines is not held up when connected unlike a modem  voice and DSL data occupy different frequency bands • The Ethernet NIC in your computer interfaces to a DSL modem • Cable Modems: Data is carried over fiber optic cables from the cable provider to the provider’s distribution hub and then over standard coaxial cable from the hub to your cable modem • Both TV signals as well as computer data are carried over the same cable • A coupler/splitter routes TV data to TV set and computer data to the cable modem GMU IT 212 - Spring 2007

  47. The Internet • History of the Internet • An interconnected system of networks that connects computers around the world via the TCP/IP protocol • Interconnected networks GMU IT 212 - Spring 2007

  48. Circuit Switching • Public switched telephone network (PSTN) uses circuit switching • Dedicated resources are allocated along the network for that particular call • No one else can use those resources, even if communication is inactive GMU IT 212 - Spring 2007

  49. Packing Switching • Internet uses packet switching • No dedicated resources allocated • Sender breaks data into packets • Packets sent across network, may go different routes • Receiver reassembles packets • Simultaneously, many other senders and receivers using the same resources http://williamstallings.com/DCC/DCC7e.html GMU IT 212 - Spring 2007

  50. Protocol layers and Encapsulation Application Layer Allows applications to work together -Example: HTTP, FTP Layer 5 Transport Layer Ensures reliable transmission, error control -Example: Transmission Control Protocol (TCP) Layer 4 Internet Layer Moves data between networks using routers using an address Example: Internet Protocol (IP) uses IP address Layer 3 Data Link Layer Moves data within a network using switches using an address -Example: Ethernet (Data Link Layer) uses MAC address Layer 2 Physical Layer Physical connection between machines including electrical signaling and wiring Example: Ethernet (Physical Layer) Layer 1 GMU IT 212 - Spring 2007

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